Summary The crew of the RobinsonR44II helicopter (registration C-FGTN, serial number10210), operated by The Helicopter Company Inc., was conducting a series of maintenance check flights following a change of the aircraft's main rotor blades. The pilot and aircraft maintenance engineer were tasked with blade tracking and the engineer had made pitch link adjustments on the main rotor blades based on the results of two earlier flights. The occurrence flight was conducted with the intention of blade tracking and checking the rotor revolutions per minute during an autorotation procedure. At approximately 1728eastern standard time, in low light conditions, the aircraft entered the autorotation at 2400feet above sea level and continued its descent until it impacted the snow-covered frozen field. The emergency locator transmitter activated and rescue and fire fighting teams responded. Both occupants suffered serious injuries and were ejected from the cockpit when the seat belt attachments failed. The aircraft was destroyed. Ce rapport est galement disponible en franais. Other Factual Information History of the Flight On 20January2007, the helicopter was flown to the Kitchener/Waterloo Regional Airport for a maintenance inspection. During the inspection, a small delamination was observed on one of the main rotor blades. The aircraft manufacturer requested that the blades be sent back to the factory and replacement blades were shipped in from Vancouver. After the new blades were installed, the aircraft maintenance engineer (AME) installed the strobe gear in preparation for blade tracking. Two maintenance check flights were conducted earlier on the day of the occurrence to track the blades; adjustments were made to one of the pitch links after each of these flights. The occurrence flight departed the Kitchener/Waterloo Regional Airport at 1722eastern standard time1 and proceeded south to the Cambridge area at 2400feet above sea level, which is approximately 1400feet above ground level (agl). The intention was to track the blades and check the rotor revolutions per minute (RPM) while the helicopter was in an autorotation. This ad hoc procedure of tracking the main rotor blades in an autorotation differed from the manufacturer's procedures listed in the aircraft section below, and was reportedly based on trouble-shooting advice received on a previous occasion. A pre-flight briefing about this procedure was limited to asking the pilot if he was comfortable doing autorotations while the AME tracked the main rotor blades. In preparation for the autorotation, the pilot flew the aircraft over open fields located southwest of Cambridge. During the autorotation, the AME's attention, which had been focused on the rotor blades, was diverted into the cockpit by an exclamation from the pilot. He observed that the engine/rotor per cent RPM gauge dual pointers were horizontal; indicating approximately 80percent, and that the aircraft was pitched nose down. There was no report of a low rotor horn or warning light which are normally set to trigger at 97percent2. The helicopter continued the descent into the snow-covered field. It struck the ground with the front section of both skids and came to rest on its left side, facing in a northerly direction. Personnel Information The pilot-in-command was certified and qualified for the flight in accordance with existing regulations and was operating in visual meteorological conditions. He received his private pilot aeroplane licence in July2000 at the Moncton Flight College. He held a commercial pilot helicopter licence (obtained in October2002) and had approximately 1300hours of total flying time; 1000hours on rotary aircraft. The commercial helicopter flight test in October2002 was conducted using the Bell206 and a pilot proficiency check for that aircraft was issued at the same time. He completed his training on the R44II helicopter on 29June2006 and obtained a licence certification of additional privileges in July2006. He had accumulated approximately 300hours on type at the time of the accident and had last conducted autorotation training in September2006. He was employed as a traffic pilot and was seated in the aircraft right seat during the occurrence flight. The pilot had previously conducted maintenance check flights on the Bell206 and theR44. The pilot was interviewed by TSB investigators; however, he did not remember any of the events pertaining to the day of the occurrence. Aircraft Information The aircraft was manufactured and imported to Canada in 2005. At the time it was flown to the Kitchener/Waterloo Regional Airport on 20January2007 for maintenance, it had accumulated a total of 1082hours. The manufacturer's procedure for in-flight track and balance of the main rotor blades is to first adjust the rotor track and balance while the helicopter is in a hover. Then the rotor track is checked at a series of increasing airspeeds. Autorotational RPM is checked after the rotor track and balance is complete. The worksheet recovered from the wreckage indicates the main rotor blades were adjusted twice following hover flights, but there was no record that the rotor tracking procedure at the various forward airspeeds had been completed. The manufacturer's procedure for checking the rotor RPM in the autorotation specifies that the helicopter be at 1900pounds gross weight or less and that three readings be taken at 500to 1000foot altitude intervals. The autorotation was initiated at 1400feet agl and the weight of the helicopter was calculated to be 2279pounds. Using the AUTOROTATION RPM chart in the manufacturer's maintenance manual and extrapolating linearly off the chart, the expected autorotation RPM would have been 110.5percent (2.5percent above the red line - 108percent). The Robinson R44II Pilot's Operating Handbook (POH) states in the Limitations section the rotor speed limits as follows: Photo 1. C-FGTN engine (E)/rotor (R) tachometer. Conservation of rotor RPM is critical to a successful autorotation in any helicopter. Once engine power is lost, the pilot must immediately lower the collective lever and establish an autorotative descent at an airspeed recommended by the manufacturer. The RobinsonR44 maintenance manual procedure for checking the rotor RPM in an autorotation specifies that the collective be held firmly against the down-stop and that a descent speed of 50knots indicated airspeed be maintained. During this procedure one of three scenarios could occur: The rotor RPM could climb and, once it showed signs of going above the green arc, the pilot would initiate a recovery to straight and level powered flight. The rotor RPM could drop and, once it showed signs of going below the green arc, the pilot would initiate a recovery to straight and level powered flight. The rotor RPM could settle somewhere in the green arc, and the pilot would initiate a recovery to straight and level powered flight. The engineer would take note of the RPM, and the helicopter would return to base for adjustments. The crew would then conduct further flight tests as described in the maintenance manual until the correct adjustment is achieved. The main rotor blade system of the RobinsonR44II helicopter is considered a low-inertia rotor system. This term refers to the tendency for the rotor to quickly deplete its stored energy when it is no longer powered. If the collective is not fully lowered, the main rotor RPM will decay causing an aerodynamic stall of the rotor system. Once the main rotor is stalled, recovery is unlikely. The POH Normal Procedures Section - Practice Autorotation contains a CAUTION which states: During simulated engine failures, rapid decreases in rotor RPM will occur, requiring immediate lowering of collective to avoid dangerously low rotor RPM. Catastrophic rotor stall could occur if rotor RPM ever drops below 80percent plus 1percent per 1000feet of altitude. Meteorological Information The aviation routine weather report (METAR) at 1700 for the Kitchener/Waterloo Regional Airport was as follows: wind 250 True (T) at 14gusting to 20knots; visibility 9statute miles (sm); sky clear; temperature -6C, dew point -12C; altimeter setting 29.50inches of mercury (in Hg); and remarks - sea level pressure 1009.0hectopascals (hPa). The METAR at 1800 was as follows: wind 250T at 16knots; visibility 9sm; few clouds at 2800feet, ceiling 3900feet overcast, 7500feet overcast; temperature -6C, dew point -12C; altimeter setting 29.53in Hg; and remarks: sea level pressure 1002.0hPa. Sunset was at 1734; the flight was conducted in low-light conditions. Safety Notices As a result of various accidents and incidents, the Robinson Helicopter Company has issued numerous safety notices. Safety Notice SN-10 states: A primary cause of accidents in light helicopters is failure to maintain rotor RPM. Low RPM rotor stall can occur at any airspeed and when it does, the rotor stops producing the lift required to support the helicopter. Safety Notice SN-10 further states: When the rotor stalls, the blades will either 'blow back' or cut off the tail cone or the rotor will just stop flying, allowing the helicopter to fall at an extreme rate. The following safety notices are relevant to this occurrence and have been included as Appendices to the report: Examination of Wreckage The helicopter struck the ground in a nose-down attitude. The forward section of the helicopter, including both front seats and seat belt attachments, was destroyed as a result of the impact. There were no pre-impact structural failures. Examination of one of the main rotor blades revealed an upward bending, with chord-wise rippling along the span and on the upper skin surface of the blade. The second blade was severely damaged from ground impacts and rippling was not evident. One of the main rotor blade's counterweight had separated from the blade tip and was found near the wreckage site. The tail rotor components were examined and found to be in serviceable condition with no pre-impact failures evident. The jam nut on the main rotor pitch link that was being adjusted was tight but not secured with lock wire. The engine compartment revealed no catastrophic failures. It was clean and free of any oil and hydraulic fluid. A variety of instruments and two global positioning systems (GPSs) were recovered from the wreckage and forwarded to the TSB Engineering Laboratory to determine the instruments readings at the time of the crash and to extract any relevant data from the GPS's non-volatile memory. The results were as follows: The rotor RPM gauge was indicating 98percent. The vertical speed indicator was indicating 800ft/min down. The manifold pressure gauge had two indications. One was in the range of 18to 19.3inches of mercury (hg.) and the other was in the range of 27.7to 29.3hg. The Lowrance Airmap 2000cGPS did not record the occurrence flight track and the Garmin Apollo SL60GPS does not retain flight track data in its non-volatile memory. The following TSB Engineering Laboratory reports were completed: LP019/2007 - Examination of Sony DVCAMLP020/2007 - Examination of Instruments These reports are available from the Transportation Safety Board of Canada upon request.